1. Field of the Invention
This invention relates to the continuous production of furfural and levulinic acid with a heat integration step.
2. Description of Related Art
The needs of the developed work are currently dependent on the utilisation of fossil fuels to produce industrial chemicals and liquid fuels. The majority of modern synthetic products are thus produced from oil. Concerns over high fuel prices, security of energy, global climate change and opportunities for rural economic development pushed governments and industries to develop what is known as first generation technologies for producing biofuels from for example maize. However due to the only marginal improvement of the effect on the climate change and the competition with food, a second generation technology was developed based on the more abundant lignocellulosic feedstocks. Many of the high potential energy crops require less energy for their production as well as less fertilizers, they result in minimal soil erosion, often increase the soil carbon content and require less water.
Lignocellulosic feedstocks are typically composed of 35 to 55% cellulose, 15 to 35% hemicellulose and 15 to 35% lignin. Lignocellulosic feedstocks can be used to produce biofuels, such as ethanol, but it is also possible to produce other chemicals. Most of the chemicals produced in both first and second generation technology are the result of fermentations. Contrary to fermentation of starch, the hydrolysis of cellulose is much more difficult and long fermentation times are needed, Often pretreatments are needed to make the cellulose accessible. M. Galbe and G. Zacchi, Appl. Microbiol. Biotechnol., (2002), 59, 618-628 and/or C. N. Hamelinck, G. van Hoojdonck, A. P. C. Faaj, Biomass and Bioenergy, (2005), 28, 384-41.0. However there are processes such as The Biofine process D. J. S. Fitzpatrick, M. H. B. Hayes, Ross, The Biofine Process—Production of levulinic Acid. Furfural, and Formic Acid from Lignocellulosic Feedstocks, “Biorefineries—Industrial Processes and Products, Volume 1, Ed. B. Kamm, P. R. Gruber, M. Kamm, Wiley-VCR, 2006, 139-163 which by contrast are entirely chemical and rely on acid catalysis and allow a wide range of lignocellulosic feedstocks to be used.
When subjecting lignocellulosic feedstock to acid treatment, the hemicellulose hydrolyses relatively easily to C5 and C6 monomers (pentose & hexose) and cellulose will hydrolyse more slowly. Depending on the source of hemicellulose it can contain acetate groups as well, which are hydrolysed to acetic acid. The lignin itself is not hydrolysed. The pentose monomers, upon farther acid treatment, can degrade to furfural, and the cellulose can hydrolyze to glucose and can farther degrade to hydroxymethylfurfural. Hydroxymethylfurfural can degrade still further in the presence of acid to levulinic acid and formic acid. Lignin together with degraded and oligomerised sugar products will end up as char and potentially as tar.
Char can be used as fertiliser or as fuel pellets. Furfural is used as a chemical or as a solvent. Formic acid and acetic acid can be used as chemicals, Levulinic acid can be used to make resins, plasticizers, chemicals, specialty chemicals, herbicides and a fuel extender, methyltetrahydrofuran.
Many plants comprising lignocellulosic materials require a lower level of water to grow and give high yields compared to food crops. Examples are grasses such as miscanthus and switch grass and wood such as poplar and willow, moreover they all have considerable amounts of cellulose and hemicellulose.
Many common waste materials include cellulose or starch. For example, primary sludges from paper manufacture, waste paper, waste wood (e.g. sawdust), as well as agricultural residues such as corn husks, corn cobs, corn stalks, rice hulls, straw and bagasse include high percentages of cellulose. Starch can be found in food processing waste derived, for example, from corn, wheat oats and barley.
U.S. Pat. No. 5,608,105 discloses a continuous process for producing levulinic acid from carbohydrate-containing materials where a carbohydrate-containing material is supplied continuously to a first reactor and hydrolyzed in the presence of a mineral acid. The hydrolysis produces hydroxymethylfurfural, which in turn is hydrolysed to give levulinic acid.
U.S. Pat. No. 4,897,497 discloses a process for producing furfural and levulinic acid from lignocellulose includes subjecting a sample of lignocellulose to several acid degradations to produce levulinic acid and furfural vapours are continuously collected from the mixture.
WO 2003/074781 discloses a process for producing furfural which utilises reactive evaporation and recycling of spent cooking liquors.
WO 2010/030617 discloses a method of recovering levulinic acid from a mixture of furfural and formic acid.